How many primaries are there?
It depends on what is meant by “primary color” because the definition varies with context. Here are 6 different ones: • Color mixing primaries (3). A viewer can combine 3 specific primaries in a comparison patch to make it appear identical in color to a sample. In additive (light) mixing, the primaries are red, green and blue. In subtractive (pigment) mixing, they are usually magenta, yellow and cyan (bright blue). Printing also uses black ink, although it is not considered a primary. Note that the color specification for primaries is vague – red might be an additive primary, but there are many distinguishable reds. Which red should you use? The answer is that any “good” red will suffice, although the amount of each primary needed will vary depending on the exact primaries used. • Color matching primaries (many). There are again 3 primaries at any given time, but in matching they can be any 3 highly saturated colors (Grassman’s first law). The only restriction is that two cannot be mix
